The proposed research will provide fundamental understanding of how transition metal complexes and active sites oxidize C-H and O-H bonds. Such chemical processes occur in a wide range of biological systems, from fatty acid oxidations by lipoxygenases to oxygen evolution by photo-system II. Many of these metalloenzymes and related systems have been individually studied in detail, but there is limited knowledge of their basic chemical reactivity underlies them. By studying a range of model compounds and model reactions, a fundamental and predictive understanding is being developed. Reactions that involve transfer of a hydrogen atom are a major focus of the studies described. The correlations of rate constants with thermodynamic driving force will be extended to new systems and with a wider range of substrates, including phenols. Factors other than driving force will be probed. Both organic radical chemistry and the Marcus theory of electron transfer will be used to provide insights. The ideas underlying this developing paradigm for hydrogen tom transfer reactions will be applied to other oxidation mechanisms, especially hydride transfer processes. The proposed work includes both mechanistic and synthetic studies. Oxidizing coordination complexes or iron, manganese, cooper, and ruthenium will be prepared and their reactions examined. These complexes are functional models for oxidizing enzymes such as lipoxygenase and dopamine beta-monooxygenase. By studying the oxidations of hydrocarbons, phenols, and other substrates in parallel with measurements of redox potentials, pK/a values, and self exchange rates, we will generate an understanding these reactions and, more generally, how metals mediate the coupled movement of protons and electrons in systems of biochemical relevance.